Digital tape recording remains a viable solution for storage of massive amounts of data. Conventionally, at least two approaches are employed for recording of digital information onto magnetic recording tape. One approach calls for moving the tape past a rotating head structure which records and plays back user information from discontinuous transverse tracks. Interactive servo systems are employed to synchronize rotation of the head structure with travel of the tape. Another approach is to draw the tape across a non-rotating head at a considerable linear velocity. This approach is sometimes referred to as linear “streaming” tape recording and playback.
Increased data storage capacity, and retrieval performance, is being required of all commercially viable mass storage devices and media. In the case of linear tape recording a popular trend is toward multi-head, multi-channel fixed head structures with narrowed recording gaps and track widths so that many linear tracks may be achieved on a tape medium of predetermined width, such as one-half inch width tape. Tape substrates are also being made thinner, with increased tape lengths being made possible in small diameter reel packages.
Because of a relatively high linear tape velocity, and because tape substrates continue to be made thinner and thinner, guiding tape past a tape head structure along an accurate invariant linear path has proven to be highly problematical. One error phenomena is known as “lateral tape motion” or “LTM”. LTM is a major source of tracking errors in linear tape recording. One approach to minimizing LTM tracking errors is to provide a multi-roller tape guide structure, such as the type described in commonly assigned U.S. Pat. No. 5,414,585 entitled: “Rotating Tape Edge Guide”, the disclosure thereof being incorporated herein by reference. While this approach has provided a viable “open loop” solution to LTM, with the advent of new head technologies, such as magneto-resistive read heads, and new higher coercivity recording media, track widths may be very small, and many additional tracks may be defined on the tape. Unfortunately, a limiting factor is LTM, and at some track width dimension and track density, it is not possible to follow the tape accurately enough to provide reliable performance.
One solution to correction for LTM has been to record or pre-record magnetic servo tracks (i.e. “servowrite”) onto the tape before it reaches the user. These tapes are known in the art as “preformatted” tapes, and the step of recording accurate servo tracks onto the tape is both time consuming and expensive. Examples of tape systems employing preformatted tapes are given by U.S. Pat. No. 5,432,652 entitled: “Servo and Data Format for Magnetic Tape Having Plural Spaced-Apart Servo Areas Interleaved with Data Track Areas Having Serpentine Track Scanning Using Any One of a Plurality of Number of Concurrently Accessed Tracks.” Another example is provided by U.S. Pat. No. 5,675,448 entitled: “Track Pitch Error Compensation System for Data Cartridge Tape Drives”.
Once the decision has been made to provide separate magnetic servo tracks or to embed servo information within the magnetic user data tracks recorded onto the tape, a suitable coarse position/fine position actuator mechanism must be added to the tape drive. One example of a stepper motor/voice coil actuator is provided by U.S Pat. No. 5,280,402 entitled: “Combined Stepper Motor and Voice Coil Head Positioning Apparatus”.
Optical servo tracks have been provided within floppy disks. One example of a floppy disk and compatible drive is given in U.S. Pat. No. 5,065,387 entitled: “Method and Apparatus for Generating Tracking Error Signals by Means of an Optical Servo System”, the disclosure thereof being incorporated herein by reference.
While these prior methods and approaches have worked within their intended applications and uses, improvements and simplifications in the medium and drive apparatus have been lacking. Accordingly, a hitherto unsolved need has remained for a multi-track, multi-channel digital streaming tape system which overcomes limitations and drawbacks of the known prior approaches.